Various types of video imaging systems are presently known and various techniques have been proposed for enhancement of video images and reduction of the bit content thereof.
Video imaging systems typically incorporate video cameras with image transmission, processing, storage, and display subsystems. These systems, some of which are described in Computer Vision, by Ballard and Brown, are designed to enhance images and to analyze them such that a computer, or other processing device, can perform other operations using information found in the image.
The amount of data required to fully describe an image is quite large and various techniques to reduce the volume of data necessary, either for image transmission or for image storage or for both, have been developed in recent years. Chapter 5 of Digital Picture Processing, by A. Rosenreid and A. Kak, discusses some of these techniques, such as transform compression techniques, which commonly achieve a 1:15 reduction in the amount of data necessary to fully describe an image. In order to display or process the compressed image, it must be expanded by an appropriate inverse operation; the exact inverse operation depends on the method of compression. Most such techniques are designed to be "lossless" in the sense that the expanded image is equal, or almost equal, to the original image before compression.
Other common techniques to enhance image transmission are decomposition techniques where the original image is decomposed into a hierarchy of images, known as "pyramidal" techniques. U.S. Pat. No. 4,674,125 to Carlson et al discloses an enhancement technique based on convolving and decimating an original high resolution image into a hierarchy of component images in which each component image comprises one octave of the spatial frequencies found in the original image and is of a higher resolution than the previous component. Another pyramidal technique decimates an original image, producing a series of images with decreasing levels of resolution, where each image has half as many pixels along each row and half as many rows as the previous image. The technique then arranges the decimated images in order of increasing resolution, producing a description of the image useful for transmission. The lowest resolution decimated image is transmitted first followed by the higher resolution images. At the receiving end, the image is reconstructed in stages where initially the lowest resolution image is displayed and subsequently, as pixels from the higher resolution images arrive, they are integrated into the image. Such pyramidal scheme is known as a Progressive Resolution scheme and it has also been applied to storage and retrieval systems.
Bit reduction in the transmission of moving images, such as in live video applications, is achieved by only transmitting the changes which occur from frame to frame. To do so, a first image is transmitted. Subsequently, successive frames are compared and any differences are extracted and transmitted. The receiving end maintains image storage and the received differences are added to the storage to produce an updated image. U.S. Pat. No. 4,716,462 to Wargo et al discloses a motion detector used to control video signal processing and functionality which operates as described hereinabove. An additional motion detector, produced as an integrated circuit, is disclosed in a publication entitled "A Correlating Optical Motion Detector" by John E. Tanner and Carver Mead of California Institute of Technology, Pasadena, Calif., published in the proceedings of the MIT Conference on Advanced Research in VLSI, 1984, pp. 57-64. The detector derives the spatio-temporal derivative of the image at the very focal plane of the image sensor and produces an image consisting of the temporal differences only.
The prior art discloses many methods and systems for reducing the bit content of images and series of images; however, none of the methods incorporates the fact that not every portion of an image contains information useful to the system user. By selecting only the high information content portion of an image, of series, of images, the amount of data necessary to describe an image such that a user can recognize it is significantly reduced. Such a method, alone or in conjunction with the reduction methods disclosed in the prior art, has many advantages over the prior aft and is the object of the present invention.